Cooling system for a computer system

ABSTRACT

The invention relates to a cooling system for a computer system, said computer system comprising at least one unit such as a central processing unit (CPU) generating thermal energy and said cooling system intended for cooling the at least one processing unit and comprising a reservoir having an amount of cooling liquid, said cooling liquid intended for accumulating and transferring of thermal energy dissipated from the processing unit to the cooling liquid. The cooling system has a heat exchanging interface for providing thermal contact between the processing unit and the cooling liquid for dissipating heat from the processing unit to the cooling liquid, Different embodiments of the heat exchanging system as well as means for establishing and controlling a flow of cooling liquid and a cooling strategy constitutes the invention of the cooling system.

This application is a continuation of U.S. application Ser. No.11/919/974, filed Jan. 6, 2009, which is a U.S. National PhaseApplication of PCT/DK2005/000310, filed May 6, 2005, which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a cooling system for a centralprocessing unit (CPU) or other processing unit of a computer system.More specifically, the invention relates to a liquid-cooling system fora mainstream computer system such as a PC.

During operation of a computer, the heat created inside the CPU or otherprocessing unit must be carried away fast and efficiently, keeping thetemperature within the design range specified by the manufacturer. As anexample of cooling systems, various CPU cooling methods exist and themost used CPU cooling method to date has been an air-coolingarrangement, wherein a heat sink in thermal contact with the CPUtransports the heat away from the CPU and as an option a fan mounted ontop of the heat sink functions as an air fan for removing the heat fromthe heat sink by blowing air through segments of the heat sink. Thisair-cooling arrangement is sufficient as long as the heat produced bythe CPU is kept at today's level, however it becomes less useful infuture cooling arrangements when considering the development of CPUssince the speed of a CPU is said to double perhaps every 18 months, thusincreasing the heat production accordingly.

Another design used today is a CPU cooling arrangement where coolingliquid is used to cool the CPU by circulating a cooling liquid inside aclosed system by means of a pumping unit, and where the closed systemalso comprises a heat exchanger past which the cooling liquid iscirculated.

A liquid-cooling arrangement is more efficient than an air-coolingarrangement and tends to lower the noise level of the coolingarrangement in general. However, the liquid-cooling design consists ofmany components, which increases the total installation time, thusmaking it less desirable as a mainstream solution. With a trend ofproducing smaller and more compact PCs for the end-users, the greateramount of components in a typical liquid-cooling arrangement is alsoundesirable. Furthermore, the many components having to be coupledtogether incurs a risk of leakage of cooling liquid from the system.

SUMMARY

It may be one object of the invention to provide a small and compactliquid-cooling solution, which is more efficient than existingair-cooling arrangements and which can be produced at a low costenabling high production volumes. It may be another object to create aliquid-cooling arrangement, which is easy-to-use and implement, andwhich requires a low level of maintenance or no maintenance at all. Itmay be still another object of the present invention to create aliquid-cooling arrangement, which can be used with existing CPU types,and which can be used in existing computer systems.

This object may be obtained by a cooling system for a computer system,said computer system comprising: at least one unit such as a centralprocessing unit (CPU) generating thermal energy and said cooling systemintended for cooling the at least one processing unit, a reservoirhaving an amount of cooling liquid, said cooling liquid intended foraccumulating and transferring of thermal energy dissipated from theprocessing unit to the cooling liquid, a heat exchanging interface forproviding thermal contact between the processing unit and the coolingliquid for dissipating heat from the processing unit to the coolingliquid, a pump being provided as part of an integrate element, saidintegrate element comprising the heat exchanging interface, thereservoir and the pump, said pump intended for pumping the coolingliquid into the reservoir, through the reservoir and from the reservoirto a heat radiating means, said heat radiating means intended forradiating thermal energy from the cooling liquid, dissipated to thecooling liquid, to surroundings of the heat radiating means.

By providing an integrate element, it is possible to limit the number ofseparate elements of the system. However, there is actually no need forlimiting the number of elements, because often there is enough spacewithin a cabinet of a computer system to encompass the differentindividual elements of the cooling system. Thus, it is surprisinglythat, at all, any attempt is conducted of integrating some of theelements.

In possible embodiments according to this aspect of the invention, theentire pump is placed inside the reservoir with at least an inlet or anoutlet leading to the liquid in the reservoir. In an alternativeembodiment the pump is placed outside the reservoir in the immediatevicinity of the reservoir and wherein at least an inlet or an outlet isleading directly to the liquid in the reservoir. By placing the pumpinside the reservoir or in the immediate vicinity outside the reservoir,the integrity of the combined reservoir, heat exchanger and pump isobtained, so that the element is easy to employ in new and existingcomputer systems, especially mainstream computer systems.

In a preferred embodiment, the pumping member of the pump and a drivenpart of the motor of the pump, such as a rotor of en electrical motor,is placed inside the reservoir embedded in the cooling liquid, andwherein a stationary part of the motor of the pump, such as a stator ofan electrical motor, is placed outside the reservoir. By having thedriven part of the motor placed inside the reservoir submerged in thecooling liquid and the stationary part of the motor outside thereservoir, there is no need for encapsulating the stationary part in aliquid-proof insulation. However, problems may occur having thenstationary part driving the driven part. However, the present inventionprovide means for obtaining such action, although not at all evident howto solve this problem.

The object may also be obtained by a cooling system for a computersystem, said computer system comprising: at least one unit such as acentral processing unit (CPU) generating thermal energy and said coolingsystem intended for cooling the at least one processing unit, areservoir having an amount of cooling liquid, said cooling liquidintended for accumulating and transferring of thermal energy dissipatedfrom the processing unit to the cooling liquid, a heat exchanginginterface for providing thermal contact between the processing unit andthe cooling liquid for dissipating heat from the processing unit to thecooling liquid, a pump intended for pumping the cooling liquid into thereservoir, through the reservoir and from the reservoir to a heatradiating means, said cooling system being intended for thermal contactwith the processing unit by means of existing fastening means associatedwith the processing unit, and said heat radiating means intended forradiating from the cooling liquid thermal energy, dissipated to thecooling liquid, to surroundings of the heat radiating means.

The use of existing fastening means has the advantage that fitting ofthe cooling system is fast and easy. However, once again there is noproblem for the person skilled in the art to adopt specially adaptedmounting means for any element of the cooling system, because there arenumerous possibilities in existing cabinets of computer systems formounting any kind of any number of elements, also elements of a coolingsystem.

In preferred embodiments according to this aspect of the invention, theexisting fastening means are means intended for attaching a heat sink tothe processing unit, or the existing fastening means are means intendedfor attaching a cooling fan to the processing unit, or the existingfastening means are means intended for attaching a heat sink togetherwith a cooling fan to the processing unit. Existing fastening means ofthe kind mentioned is commonly used for air cooling of CPUs of computersystems, however, air cooling arrangements being much less complex thanliquid cooling systems. Nevertheless, it has ingeniously been possibleto develop a complex and effective liquid cooling system capable ofutilizing such existing fastening means for simple and less effectiveair cooling arrangements.

According to an aspect of the invention, the pump is selected from thefollowing types: Bellows pump, centrifugal pump, diaphragm pump, drumpump, flexible liner pump, flexible impeller pump, gear pump,peristaltic tubing pump, piston pump, processing cavity pump, pressurewasher pump, rotary lobe pump, rotary vane pump and electro-kineticpump. By adopting one or more of the solution of the present invention,a wide variety of pumps may be used without departing from the scope ofthe invention.

According to another aspect of the invention, driving means for drivingthe pump is selected among the following driving means: electricallyoperated rotary motor, piezo-electrically operated motor, permanentmagnet operated motor, fluid-operated motor, capacitor-operated motor.As is the case when selecting the pump to pump the liquid, by adoptingone or more of the solution of the present invention, a wide variety ofpumps may be used without departing from the scope of the invention.

The object may also be obtained by a cooling system for a computersystem, said computer system comprising: at least one unit such as acentral processing unit (CPU) generating thermal energy and said coolingsystem intended for cooling the at least one processing unit, areservoir having an amount of cooling liquid, said cooling liquidintended for accumulating and transferring of thermal energy dissipatedfrom the processing unit to the cooling liquid, a heat exchanginginterface for providing thermal contact between the processing unit andthe cooling liquid for dissipating heat from the processing unit to thecooling liquid, a pump intended for pumping the cooling liquid into thereservoir, through the reservoir and from the reservoir to a heatradiating means, and said cooling system further comprising a pumpwherein the pump is driven by an AC electrical motor by a DC electricalpower supply of the computer system, where at least part of theelectrical power from said power supply is intended for being convertedto AC being supplied to the electrical motor.

It may be advantageous to use an AC motor, such as a 12V AC motor, fordriving the pump in order to obtain a stabile unit perhaps having tooperate 24 hours a day, 365 days a year. However, the person skilled inthe art will find it unnecessary to adopt as example a 12V motor becausehigh voltage such as 220V or 110V is readily accessible as this is theelectrical voltage used to power the voltage supply of the computersystem itself. Although choosing to use a 12V motor for the pump, it hasnever been and will never be the choice of the person skilled in the artto use an AC motor. The voltage supplied by the voltage supply of thecomputer system itself is DC, thus this will be the type of voltagechosen by the skilled person.

In preferred embodiments according to any aspect of the invention, anelectrical motor is intended both for driving the pump for pumping theliquid and for driving the a fan for establishing a flow of air in thevicinity of the reservoir, or an electrical motor is intended both fordriving the pump for pumping the liquid and for driving the a fan forestablishing a flow of air in the vicinity of the heat radiating means,or an electrical motor is intended both for driving the pump for pumpingthe liquid, and for driving the a fan for establishing a flow of air inthe vicinity of the reservoir, and for driving the a fan forestablishing a flow of air in the vicinity of the heat radiating means.

By utilizing a single electrical motor for driving more than one elementof the cooling system according to any of the aspects of the invention,the lesser complexity and the reliability of the cooling system will befurther enhanced.

The heat exchanging interface may be an element being separate from thereservoir, and where the heat exchanging interface is secured to thereservoir in a manner so that the heat exchanging interface constitutespart of the reservoir when being secured to the reservoir.Alternatively, the heat exchanging interface constitutes an integratesurface of the reservoir, and where the heat exchanging surface extendsalong an area of the surface of the reservoir, said area of surfacebeing intended for facing the processing unit and said area of surfacebeing intended for the close thermal contact with the processing unit.Even alternatively, the heat exchanging interface is constitutes by afree surface of the processing unit, and where the free surface iscapable of establishing heat dissipation between the processing unit andthe cooling liquid through an aperture provided in the reservoir, andwhere the aperture extends along an area of the surface of thereservoir, said surface being intended for facing the processing unit.

Possibly, an uneven surface such as pins or fins extending from thecopper plate provide a network of channels across the inner surface ofthe heat exchanging interface. A network of channels ensure the coolingliquid being passed along the inner surface of the interface such as acopper plate in a way that maximizes the retention time of the coolingliquid along the heat exchanging interface and in a way that optimizesthe thermal exchange between the heat exchanging interface and thecooling liquid as long as the cooling liquid is in thermal contact withheat exchanging interface.

Possibly, the cooling system may be provided with a heat exchanginginterface for providing thermal contact between the processing unit andthe cooling liquid for dissipating heat from the processing unit to thecooling liquid, a pumping means being intended for pumping the coolingliquid into the reservoir, through the reservoir and from the reservoirto a heat radiating means, said heat radiating means intended forradiating thermal energy from the cooling liquid, dissipated to thecooling liquid, to surroundings of the heat radiating means, said heatexchanging interface constituting a heat exchanging surface beingmanufactured from a material suitable for heat conducting, and with afirst side of the heat exchanging surface facing the central processingunit being substantially plane and with a second side of the heatexchanging surface facing the cooling liquid being substantially planeand said reservoir being manufactured from plastic, and channels orsegments being provided in the reservoir for establishing a certainflow-path for the cooling liquid through the reservoir.

Providing a plane heat exchanging surface, both the first, inner sidebeing in thermal contact with the cooling liquid and the second, outerside being in thermal contact with the heat generating processing unit,results in the costs for manufacturing the heat exchanging surface isreduced to an absolute minimum.

According to the above possible solution, an inlet of the pumping meansis positioned in immediate vicinity of the heat exchanging interface forthereby obtaining a turbulence of flow of the cooling liquid in theimmediate vicinity of the heat exchanging interface. The turbulence offlow is advantageous for obtaining a heat dissipation. If the heatexchanging interface is plane, the inlet of the pump being positioned asmentioned above, may result in a turbulence of flow occurring along theheat exchanging interface, at least in the vicinity of the inlet of thepump, but possibly also distant form the inlet.

Alternatively, or additionally, an outlet of said pumping means beingpositioned in immediate vicinity of the heat exchanging interface forthereby obtaining a turbulence of flow of the cooling liquid in theimmediate vicinity of the heat exchange interface. The turbulence offlow is advantageous for obtaining a heat dissipation. If the heatexchanging interface is plane, the inlet of the pump being positioned asmentioned above, may result in a turbulence of flow occurring along theheat exchanging interface, at least in the vicinity of the inlet of thepump, but possibly also distant form the inlet.

However, a plane first, inner surface may also result in the coolingliquid passing the heat exchanging surface too fast. This may beremedied by providing grooves along the inner surface, thereby providinga flow path in the heat exchanging surface. This however results in thecosts for manufacturing the heat exchanging surface increasing.

The solution to this problem has been dealt with by providing channelsor segments in the reservoir housing instead. The reservoir housing maybe manufactured by injection molding or by casting, depending on thematerial which the reservoir housing is made from. Proving channels orsegments during molding or casting of the reservoir housing is much morecost-effective than milling grooves along the inner surface of the heatexchanging surface.

Possibly, the cooling system may be provided with at least one liquidreservoir mainly for dissipating or radiating heat, said heat beingaccumulated and transferred by said cooling liquid, said cooling systembeing adapted such as to provide transfer of said heat from a heatdissipating surface to a heat radiating surface where said at least oneliquid reservoir being provided with one aperture intended for beingclosed by placing said aperture covering part of, alternatively coveringthe whole of, the at least one processing unit in such a way that a freesurface of the processing unit is in direct heat exchanging contact withan interior of the reservoir, and thus in direct heat exchanging contactwith the cooling liquid in the reservoir, through the aperture.

Heat dissipation from the processing unit to the cooling liquid must bevery efficient to ensure proper cooling of the processing unit,Especially in the case, where the processing unit is a CPU, the surfacefor heat dissipation is limited by the surface area of the CPU. This maybe remedied by utilizing a heat exchanging surface being made of amaterial having a high thermal conductivity such as copper or aluminumand ensuring a proper thermal bondage between the heat exchanginginterface and the CPU.

However, in a possible embodiment according to the features in the aboveparagraph, the heat dissipation takes place directly between theprocessing unit and the cooling liquid by providing an aperture in thereservoir housing, said aperture being adapted for taking up a freesurface of the processing unit. Thereby, the free surface of theprocessing unit extends into the reservoir or constitutes a part of theboundaries of the reservoir, and the cooling liquid has direct access tothe free surface of the processing unit.

A possible heat exchanging interface may be the direct contact betweenthe heat generating unit such as a CPU and the cooling liquid, where atleast one unit such as a central processing unit (CPU) generatingthermal energy and said cooling system intended for cooling the at leastone processing unit comprising at least one liquid reservoir mainly fordissipating or radiating heat, said heat being accumulated andtransferred by said cooling liquid, said cooling system being adaptedsuch as to provide transfer of said heat from a heat dissipatinginterface to a heat radiating surface where said at least one liquidreservoir being provided with one aperture intended for being closed byplacing said aperture covering part of, alternatively covering the wholeof, the at least one processing unit in such a way that a free surfaceof the processing unit is in direct heat exchanging contact with aninterior of the reservoir, and thus in direct heat exchanging contactwith the cooling liquid in the reservoir, through the aperture.

The aperture of the reservoir may be intended for being closed byattaching boundaries of said aperture to a free surface of a theprocessing unit, said boundaries being liquid-proof when attached to thefree surface of the processing unit so that the liquid may flow freelyacross the free surface without the risk of the liquid dissipatingthrough the boundaries. Alternatively, but posing the same technicaleffect, the aperture of the reservoir is intended for being closed byattaching boundaries of said aperture along boundaries of a free surfaceof the processing unit.

If a heat sink is provided as an aid in dissipating heat from the heatgenerating unit such as a CPU, the aperture of the reservoir may beintended for being closed by attaching boundaries of said aperture to afree surface of a heat sink. Alternatively, the aperture of thereservoir may be intended for being closed by attaching boundaries ofsaid aperture along boundaries of a free surface of a heat sink.Alternatively, possibly, the heat exchanging interface may be providedas a first reservoir intended for being closed by attaching boundariesof an aperture in the first reservoir to, alternatively along, a freesurface of a said processing unit, and a second reservoir intended forbeing closed by attaching boundaries of an aperture in the secondreservoir to, alternatively along, a free surface of a to a free surfaceof a heat sink, and liquid conducting means provided between the firstreservoir and the second reservoir.

The first reservoir may be closed by attaching said first reservoir to aheat exchanging surface element being in close thermal contact with theprocessing unit, said heat exchanging surface intended for dissipatingheat from the processing unit to cooling liquid in the first reservoir,and wherein a second reservoir is closed by attaching said secondreservoir to a surface of a heat sink, said heat sink intended forradiating heat from cooling liquid in the second reservoir to theexterior surroundings.

Also, the first reservoir and said second reservoir may be provided as amonolithic structure comprising both the first reservoir and the secondreservoir and where both a heat dissipation from the processing unit tothe cooling liquid in the first reservoir and heat radiation from thecooling liquid in the second reservoir to exterior surrounding isprovided by the monolithic structure. The said monolithic structure maypreferably be manufactured at least partly from plastic, preferablybeing manufactured fully in plastic, and said monolithic structure thusbeing manufactured by injection molding.

Transfer of said cooling liquid from an outlet of the first reservoir toan inlet of the second reservoir, and from an outlet of the secondreservoir to an inlet of the first reservoir, and circulating thecooling liquid within said liquid conducting means is provided by apumping means being intended for pumping the cooling liquid. One of saidreservoirs of said monolithic structure may comprise said pumping means.

An inlet and/or an outlet and/or a pumping member of said pumping means,may be provided in the vicinity of said substantially plane side inorder to provide a turbulence of flow and hereby improve the exchange ofheat between said cooling liquid and substantially plane side, and theinlet of the pumping means may be provided within the first reservoirand the outlet may be provided within the second reservoir.

According to one aspect of the invention, a method is envisaged, saidmethod of cooling a computer system comprising at least one unit such asa central processing unit (CPU) generating thermal energy and saidmethod utilizing a cooling system for cooling the at least oneprocessing unit and, said cooling system comprising a reservoir, atleast one heat exchanging interface and a pumping means, said method ofcooling comprising the steps of establishing, or defining, or selectingan operative status of the pumping means; controlling the operation ofthe motor of the pumping means in response to the following parameters;the necessary direction of movement for obtaining a pumping action of apumping member of the pumping means, the possible direction of movementof a driving part of the motor of the pumping means; and in accordancewith the operative status being established, defined or selected,controlling the operation of the computer system in order to achieve thenecessary direction of movement of the driving part of the motor forestablishing the necessary direction of movement for obtaining hepumping action of the pumping member.

There may be pumping means, where the pumping member is only operable inone direction but where the motor driving the pumping member is operablein two directions. The solution to this problem is to either choose apumping member operable in both directions or to chose a motor beingoperable in only one direction. According to the invention, a solutionis provided where a one-way directional pumping member may be operatedany a two-way directional motor. Despite the contradictory nature ofthis solution, advantages may however be present.

As example, the method is being applied to a cooling system where thepumping member is a rotary impeller having a one-way direction forobtaining a pumping action, and where the motor of the pumping means isan electrical AC motor having a rotor constituting the driving part ofthe motor, and where said method comprises the step of establishing, ordefining, or selecting a rotary position of the rotor of the electricalAC motor, and applying at least one half-wave of an AC power signal tothe stator of the AC motor before applying a full-wave AC power signal.

As an alternative example, the method is being applied to a coolingsystem where the pumping member is a rotary impeller having a one-waydirection for obtaining a pumping action, and where the motor of thepumping means is an electrical AC motor having a rotor constituting thedriving part of the motor, and said method comprises the step ofestablishing, or defining, or selecting a rotary position of the rotorof the electrical AC motor, and applying at least one half-wave of an ACpower signal to the stator of the AC motor after having applied thefull-wave AC power signal.

In both the above examples, the advantages of the one-way impeller froma traditional DC pump together with the advantages of a motor from atraditional AC pump is obtained in the solution mentioned. Theperformance of an impeller of a DC pump is much better than theperformance of an impeller from an AC pump. The motor from an AC pump ismore reliable than a motor from a DC pump. The advantageous obtained isthus of synergetic nature, seeing that different advantages of theimpeller of the DC pump and of the motor of the AC pump are different innature.

According to another aspect of the invention, a method is envisaged,said method of cooling a computer system comprising at least one unitsuch as a central processing unit (CPU) generating thermal energy andsaid method utilizing a cooling system for cooling the at least oneprocessing unit and, said cooling system comprising a reservoir, atleast one heat exchanging interface, an air blowing fan, a pumpingmeans, said method of cooling comprising the steps of applying one ofthe following possibilities of how to operate the computer system:establishing, or defining, or selecting an operative status of thecomputer system; controlling the operation of at least one of thefollowing means of the computer system; the pumping means and the airblowing fan in response to at least one of the following parameters; asurface temperature of the heat generating processing unit, an internaltemperature of the heat generating processing unit, or a processing loadof the CPU; and in accordance with the operative status beingestablished, defined or selected, controlling the operation of thecomputer system in order to achieve at least one of the followingconditions; a certain cooling performance of the cooling system, acertain electrical consumption of the cooling system, a certain noiselevel of the cooling system.

Applying the above method ensures an operation of the computer systembeing in accordance with selected properties during the use of thecomputer system. For some applications, the cooling performance is vitalsuch as may be the case when working with image files or whendownloading large files from a network during which the processing unitsis highly loaded and thus generating much heat. For other applications,the electrical power consumption is more vital such as may be the casewhen utilizing domestic computer systems or in large office building inenvironments where the electrical grid may be weak such as in thirdcountries. In still other applications, the noise generated by thecooling system is to be reduced to a certain level, which may be thecase in office buildings with white collar people working alone, or athome, if the domestic computer perhaps is situated in the living room,or at any other location where other exterior considerations have to bedealt with.

According to another aspect of the invention, a method is envisaged,said method being employed with cooling system further comprising apumping means with an impeller for pumping the cooling liquid through apumping housing, said pumping means being driven by an AC electricalmotor with a stator and a rotor, and said pumping means being providedwith a means for sensing a position of the rotor, and wherein the methodcomprises the following steps: initially establishing a preferredrotational direction of the rotor of the electrical motor; before startof the electrical motor, sensing the angular position of the rotor;during start, applying an electrical AC voltage to the electrical motorand selecting the signal value, positive or negative, of the AC voltageat start of the electrical motor; said selection being made according tothe preferred rotational direction; and said application of the ACsignal, such as an AC voltage, being performed by the computer systemfor applying the AC signal, such as an AC voltage, from the electricalpower supply of the computer system during conversions of the electricalDC signal, such as a DC voltage, of the power supply to the AC signal,such as an AC voltage, for the electrical motor.

Adopting the above method according to the invention ensures the mostefficient circulation of cooling liquid in the cooling system and at thesame time ensures the lowest possible energy consumption of theelectrical motor driving the impeller. The efficient circulation of thecooling liquid is obtained by means of an impeller being designed forrotation in one rotational direction only, thus optimizing the impellerdesign with regard to the only one rotational direction as opposed toboth rotational directions. The low energy consumption is achievedbecause of the impeller design being optimized, thus limiting thenecessary rotational speed of the impeller for obtaining e certainamount of flow of the cooling liquid through the cooling system. A bonuseffect of the lowest possible energy consumption being obtained is thelowest possible noise level of the pump also being obtained. The noiselevel of the pump is amongst other parameters also dependent on thedesign and the rotational speed of the impeller. Thus, an optimizedimpeller design and impeller speed will reduce the noise level to thelowest possible in consideration of ensuring a certain cooling capacity.

BRIEF DESCRIPTION OF THE FIGURES

The invention will hereafter be described with reference to thedrawings, where

FIG. 1 shows an embodiment of the prior art. The figure shows thetypical components in an air-cooling type CPU cooling arrangement.

FIG. 2 shows an embodiment of the prior art. The figure shows the partsof the typical air-cooling type CPU cooling arrangement of FIG. 1 whenassembled.

FIG. 3 shows an embodiment of the prior art. The figure shows thetypical components in a liquid-cooling type CPU cooling arrangement.

FIG. 4 is an exploded view of the invention and the surroundingelements.

FIG. 5 shows the parts shown in the previous figure when assembled andattached to the motherboard of a computer system.

FIG. 6 is an exploded view of the reservoir from the previous FIGS. 4and 5 seen from the opposite site and also showing the pump.

FIG. 7 is a cut-out view into the reservoir housing the pump and aninlet and an outlet extending out of the reservoir.

FIG. 8 is a view of the cooling system showing the reservoir connectedto the heat radiator.

FIG. 9-10 are perspective views of a possible embodiment of reservoirhousing providing direct contact between a CPU and a cooling liquid in areservoir.

FIG. 11-13 are perspective views of a possible embodiment of heat sinkand a reservoir housing constituting an integrated unit.

FIG. 14 is a perspective view of the embodiment shown in FIG. 9-10 andthe embodiment shown in FIG. 11-13 all together constituting anintegrated unit.

FIG. 15-16 are perspective view of a possible embodiment of a reservoirand a pump and a heat exchanging surface constituting an integrated unit

FIG. 17 is a perspective view of a preferred embodiment of a reservoirand a pump and a heat exchanging surface constituting an integratedunit.

FIG. 18 is a plane view of a possible, however preferred embodiment ofan AC electrical motor for a pumping means of the cooling systemaccording to the invention, and

FIG. 19 is a graph showing a method for starting a rotor of theelectrical AC motor, said AC motor driving an impeller selected from apump driven by a DC motor.

FIG. 20 is a is a simplified schematic showing a cross-sectional view ofthe reservoir along plane 20-20 of FIG. 17.

DETAILED DESCRIPTION

FIG. 1 is an exploded view of an embodiment of prior art coolingapparatus for a computer system. The figure shows the typical componentsin an air-cooling type CPU cooling arrangement. The figure shows a priorart heat sink 4 intended for air cooling and provided with segmentsintersected by interstices, a prior art air fan 5 which is to be mountedon top of the heat sink by use of fastening means 3 and 6.

The fastening means comprises a frame 3 provided with holes intended forbolts, screws, rivets or other suitable fastening means (not shown) forthereby attaching the frame to a motherboard 2 of a CPU 1 or ontoanother processing unit of the computer system. The frame 3 is alsoprovided with mortises provided in perpendicular extending studs in eachcorner of the frame, said mortises intended for taking up tenons of acouple of braces. The braces 6 are intended for enclosing the heat sink4 and the air fan 5 so that the air fan and the heat sink thereby issecured to the frame. Using proper retention mechanisms, when the frameis attached to the motherboard of the CPU of other processing unit, andwhen the tenons of the braces are inserted into the mortises of theframe, the air fan and heat exchanger is pressed towards the CPU byusing a force perpendicular to the CPU surface, said force beingprovided by lever arms.

FIG. 2 shows the parts of the typical air-cooling type CPU coolingarrangement of FIG. 1, when assembled. The parts are attached to eachother and will be mounted on top of a CPU on a motherboard (not shown)of a computer system.

FIG. 3 shows another embodiment of a prior art cooling system. Thefigure shows the typical components in a liquid-cooling type CPU coolingarrangement. The figure shows a prior art heat exchanger 7, which is inconnection with a prior art liquid reservoir 8, a prior art liquid pump9 and a heat radiator 11 and an air fan 10 provided together with theheat radiator. The prior art heat exchanger 7, which can be mounted on aCPU (not shown) is connected to a radiator and reservoir, respectively.The reservoir serves as a storage unit for excess liquid not capable ofbeing contained in the remaining components. The reservoir is alsointended as a means for venting the system of any air entrapped in thesystem and as a means for filling the system with liquid. The heatradiator 11 serves as a means for removing the heat from the liquid bymeans of the air fan 10 blowing air through the heat radiator. All thecomponents are in connection with each other via tubes for conductingthe liquid serving as the cooling medium.

FIG. 4 is an exploded view of a cooling system according to anembodiment of the invention. Also elements not being part of the coolingsystem as such are shown. The figure shows a central processing unit CPU1 mounted on a motherboard of a computer system 2. The figure also showsa part of the existing fastening means, i.e. amongst others the frame 3with mortises provided in the perpendicular extending studs in eachcorner of the frame. The existing fastening means, i.e. the frame 3 andthe braces 6, will during use be attached to the motherboard 2 by meansof bolts, screws, rivets or other suitable fastening means extendingthrough the four holes provided in each corner of the frame andextending through corresponding holes in the motherboard of the CPU. Theframe 3 will still provide an opening for the CPU to enable the CPU toextend through the frame.

The heat exchanging interface 4 is a separate element and is made of aheat conducting material having a relative high heat thermalconductivity such as copper or aluminum, and which will be in thermalcontact with the CPU 1, when the cooling system is fastened to themotherboard 2 of the CPU. The heat exchanging surface constitutes partof a liquid reservoir housing 14, thus the heat exchanger 4 constitutesthe part of the liquid reservoir housing facing the CPU. The reservoirmay as example be made of plastic or of metal. The reservoir or anyother parts of the cooling system, which are possibly manufactured froma plastic material may be “metalized” in order to minimize liquiddiffusion or evaporation of the liquid. The metal may be provided as athin layer of metal coating provided on either or on both of theinternal side or the external side of the plastic part.

If the reservoir is made of metal or any other material having arelative high heat conductivity compared to as example plastic, the heatexchanging interface as a separate element may be excluded because thereservoir itself may constitute a heat exchanger over an area, whereinthe reservoir is in thermal contact with the processing unit.Alternatively to having the heat exchanging interface constitute part ofthe liquid reservoir housing, the liquid reservoir housing may betightly attached to the heat exchanging interface by means of screws,glue, soldering, brazing or the like means for securing the heatexchanging interface to the housing and vice versa, perhaps with asealant 5 provided between the housing and the heat exchanginginterface.

Alternatively to providing a heat exchanging interface integrate withthe reservoir containing the cooling liquid, it will be possible toexclude the heat exchanger and providing another means for dissipatingheat from the processing unit to the cooling liquid in the reservoir.The other means will be a hole provided in the reservoir, said holeintended for being directed towards the processing unit. Boundaries ofthe hole will be sealed towards boundaries of the processing unit orwill be sealed on top of the processing unit for thereby preventingcooling liquid from the reservoir from leaking. The only prerequisite tothe sealing is that a liquid-tight connection is provided betweenboundaries of the hole and the processing unit or surrounding of theprocessing unit, such as a carrier card of the processing unit.

By excluding the heat exchanger, a more effective heat dissipation willbe provided from the processing unit and to the cooling liquid of thereservoir, because the intermediate element of a heat exchanger iseliminated. The only obstacle in this sense is the provision of asealing being fluid-tight in so that the cooling liquid in the reservoiris prevented from leaking.

The heat exchanging surface 4 is normally a copper plate. When excludingthe heat exchanging surface 4, which may be a possibility not only forthe embodiments shown in FIG. 4, but for all the embodiments of theinvention, it may be necessary to provide the CPU with a resistantsurface that will prevent evaporation of the cooling liquid and/or anydamaging effect that the cooling liquid may pose to the CPU. A resistantsurface may be provided the CPU from the CPU producer or it may beapplied afterwards. A resistant surface to be applied afterwards maye.g. be a layer, such as an adhesive tape provided on the CPU. Theadhesive tape may be made with a thin metal layer e.g. in order toprevent evaporation of the cooling liquid and/or any degeneration of theCPU itself.

Within the liquid reservoir, a liquid pump (not shown) is placed forpumping a cooling liquid from an inlet tube 15 connection being attachedto the housing of the reservoir through the reservoir and past the heatexchanger in thermal contact with the CPU to an outlet tube connection16 also being attached to the reservoir housing. The existing fasteningmeans comprising braces 6 with four tenons and the frame 3 with fourcorresponding mortises will fasten the reservoir and the heat exchangerto the motherboard of the CPU. When fastening the two parts of theexisting fastening means to each other the fastening will by means ofthe lever arms 18 create a force to assure thermal contact between theCPU 1 mounted on the motherboard and the heat exchanger 4 being providedfacing the CPU.

The cooling liquid of the cooling system may be any type of coolingliquid such as water, water with additives such as anti-fungicide, waterwith additives for improving heat conducting or other specialcompositions of cooling liquids such as electrically non-conductiveliquids or liquids with lubricant additives or anti-corrosive additives.

FIG. 5 shows the parts shown in FIG. 4 when assembled and attached tothe motherboard of a CPU of a computer system 2. The heat exchanger andthe CPU is in close thermal contact with each other. The heat exchangerand the remainder of the reservoir housing 14 is fastened to themotherboard 2 by means of the existing fastening means being secured tothe motherboard of the CPU and by means of the force established by thelever arms 18 of the existing fastening means. The tube inlet connection15 and the tube outlet connection 16 are situated so as to enableconnection of tubes to the connections.

FIG. 6 is an exploded view of the reservoir shown in previous FIG. 4 andFIG. 5 and seen from the opposite site and also showing the pump 21being situated inside the reservoir. Eight screws 22 are provided forattaching the heat exchanging surface 4 to the remainder of thereservoir. The heat exchanging surface is preferably made from a copperplate having a plane outer surface as shown in the figure, said outersurface being intended for abutting the free surface of the heatgenerating component such as the CPU (see FIG. 4). However, also theinner surface (not shown, see FIG. 7) facing the reservoir is plane.Accordingly, the copper plate need no machining other than the shapingof the outer boundaries into the octagonal shape used in the embodimentshown and drilling of holes for insertion of the bolts. No milling ofthe inner and/or the outer surface need be provided.

A sealant in form of a gasket 13 is used for the connection between thereservoir housing 14 and the heat exchanging surface forming a liquidtight connection. The pump is intended for being placed within thereservoir. The pump has a pump inlet 20 through which the cooling liquidflows from the reservoir and into the pump, and the pump has a pumpoutlet 19 through which the cooling liquid is pumped from the pump andto the outlet connection. The figure also shows a lid 17 for thereservoir. The non-smooth inner walls of the reservoir and the fact thatthe pump is situated inside the reservoir will provide a swirling of thecooling liquid inside the reservoir.

However, apart from the non-smooth walls of the reservoir and the pumpbeing situated inside the reservoir, the reservoir may be provided withchannels or segments for establishing a certain flow-path for thecooling liquid through the reservoir (see FIG. 9-10 and FIG. 15).Channel or segments are especially needed when the inner surface of theheat exchanging surface is plane and/or when the inner walls of thereservoir are smooth and/or if the pump is not situated inside thereservoir. In either of the circumstances mentioned, the flow of thecooling liquid inside the reservoir may result in the cooling liquidpassing the reservoir too quickly and not being resident in thereservoir for a sufficient amount of time to take up a sufficient amountof heat from the heat exchanging surface. By providing channels orsegments inside the reservoir, a flow will be provided forcing thecooling liquid to pass the heat exchanging surface, and the amount oftime increased of the cooling liquid being resident inside thereservoir, thus enhancing heat dissipation. If channels or segments areto be provided inside the reservoir, the shape and of the channels andsegments may be decisive of whether the reservoir is to be made ofplastic, perhaps by injection molding, or is to be made of metal such asaluminum, perhaps by die casting.

The cooling liquid enters the reservoir through the tube inletconnection 15 and enters the pump inlet 20, and is pumped out of thepump outlet 19 connected to the outlet connection 16. The connectionbetween the reservoir and the inlet tube connection and the outlet tubeconnection, respectively, are made liquid tight. The pump may not onlybe a self-contained pumping device, but may be made integrated into thereservoir, thus making the reservoir and a pumping device one singleintegrated component. This single integrated element of the reservoirand the pumping device may also be integrated, thus making thereservoir, the pumping device and the heat exchanging surface one singleintegrated unit. This may as example be possible if the reservoir ismade of a metal such as aluminum. Thus, the choice of material providesthe possibility of constituting both the reservoir and a heat exchangingsurface having a relatively high heat conductivity, and possibly alsorenders the possibility of providing bearings and the likeconstructional elements for a motor and a pumping wheel being part ofthe pumping device.

In an alternative embodiment, the pump is placed in immediate vicinityof the reservoir, however outside the reservoir. By placing the pumpoutside, but in immediate vicinity of the reservoir, still an integrateelement may be obtained. The pump or the inlet or the outlet ispreferably positioned so as to obtain a turbulence of flow in theimmediate vicinity of the heat exchanging interface, thereby promotingincreased heat dissipation between the heat exchanging interface end thecooling liquid even in the alternative, a pumping member such as animpeller (see FIG. 15-16) may be provided in the immediate vicinity ofthe heat exchanging surface. The pumping member itself normallyintroduces a turbulence of flow, and thereby the increased heatdissipation is promoted irrespective of the position of the pump itself,or the position of the inlet or of the outlet to the reservoir or to thepump.

The pump may be driven by an AC or a DC electrical motor. When driven byan AC electrical motor, although being technically and electricallyunnecessary in a computer system, this may be accomplished by convertingpart of the DC electrical power of the power supply of the computersystem to AC electrical power for the pump. The pump may be driven by anelectrical motor at any voltage common in public electrical networkssuch as 110V or 220V. However, in the embodiment shown, the pump isdriven by a 12V AC electrical motor.

Control of the pump in case the pump is driven by an AC electricalmotor, preferably takes place by means of the operative system or analike means of the computer system itself, and where the computer systemcomprises means for measuring the CPU load and/or the CPU temperature.Using the measurement performed by the operative system or alike systemof the computer system eliminates the need for special means foroperating the pump. Communication between the operative system or alikesystem and a processor for operating the pump may take place alongalready established communication links in the computer system such as aUSB-link. Thereby, a real-time communication between the cooling systemand the operative system is provided without any special means forestablishing the communication.

In the case of the motor driving the pump is an AC electrical motor, theabove method of controlling the pump may be combined with a method,where said pumping means is provided with a means for sensing a positionof the rotor of the electrical motor, and wherein the following stepsare employed: Initially establishing a preferred rotational direction ofthe rotor of the electrical motor, before start of the electrical motor,sensing the angular position of the rotor, during start, applying anelectrical AC voltage to the electrical motor and selecting the signalvalue, positive or negative, of the AC voltage at start of theelectrical motor, said selection being made according to the preferredrotational direction, and said application of the AC voltage beingperformed by the computer system for applying the AC voltage from theelectrical power supply of the computer system during conversion of theelectrical DC voltage of the power supply to AC voltage for theelectrical motor. By the operative system of the computer system itselfgenerating the AC voltage for the electrical motor, the rotationaldirection of the pump is exclusively selected by the computer system,non-depending on the applied voltage of the public grid powering thecomputer system.

Further control strategies utilizing the operative system or alikesystem of the computer system may involve balancing the rotational speedof the pump as a function of the cooling capacity needed. If a lowercooling capacity is needed, the rotational speed of the pump, may belimited, thereby limiting the noise generating by the motor driving thepump.

In the case an air fan is provided in combination with a heat sink asshown in FIG. 1, of the air fan is provided in combination with the heatradiator, the operative system or alike system of the computer systemmay be designed for regulating the rotational speed of the pump, andthus of the motor driving the pump, and the rotational speed of the airfan, and thus the motor driving the air fan. The regulation will takeinto account the cooling capacity needed, but the regulation will at thesame time take into account which of the two cooling means, i.e. thepump and the air fan, is generating the most noise. Thus, it the air fangenerally is generating more noise than the pump, then the regulationwill reduce the rotational speed of the air fan before reducing therotational speed of the pump, whenever a lower cooling capacity isneeded. Thereby, the noise level of the entire cooling system is loweredas much as possible. If the opposite is the case, i.e. the pumpgenerally generating more noise than the air fan, then the rotationalspeed of the pump will be reduced before reducing the rotational speedof the air fan.

Even further control strategies involve controlling the cooling capacityin dependence on the type of computer processing taking place. Some kindof computer processing, such as word-processing, applies a smaller loadon the processing units such as the CPU than other kinds of computerprocessing, such as image processing. Therefore, the kind of processingtaking place on the computer system may be used as an indicator of thecooling capacity. It may even be possible as part of the operativesystem or similar system to establish certain cooling scenarios,depending on the kind of processing intended by the user. If the userselects as example word-processing, a certain cooling strategy isapplied based on a limited need for cooling. If the user selects asexample image-processing, a certain cooling strategy is applied based onan increased need for cooling. Two or more different cooling scenariosmay be established depending on the capacity and the controlpossibilities and capabilities of the cooling system and depending onthe intended use of the computer system, either as selected by a userduring use of the computer system or as selected when choosing hardwareduring build-up of the computer system, i.e. before actual use of thecomputer system.

The pump is not being restricted to a mechanical device, but can be inany form capable of pumping the cooling liquid through the system.However, the pump is preferably one of the following types of mechanicalpumps: Bellows pump, centrifugal pump, diaphragm pump, drum pump,flexible liner pump, flexible impeller pump, gear pump, peristaltictubing pump, piston pump, processing cavity pump, pressure washer pump,rotary lobe pump, rotary vane pump and electro-kinetic pump. Similarly,the motor driving the pumping member need not be electrical but may alsobe a piezo-electrically operated motor, a permanent magnet operatedmotor, a fluid-operated motor or a capacitor-operated motor. The choiceof pump and the choice of motor driving the pump id dependent on manydifferent parameters, and it is up to the person skilled in the art tochoose the type of pump and the type of motor depending on the specificapplication. As example, some pumps and some motors are better suitedfor small computer systems such as lab-tops, some pumps and some motorsare better suited for establishing high flow of the cooling liquid andthus a high cooling effect, and even some pumps and motors are bettersuited for ensuring a low-noise operation of the cooling system.

FIG. 7 is a cut-out view into the reservoir, when the reservoir and theheat exchanging surface 4 is assembled and the pump 21 is situatedinside the reservoir. The reservoir is provided with the tube inletconnection (not seen from the figure) through which the cooling liquidenters the reservoir. Subsequently, the cooling liquid flows through thereservoir passing the heat exchanging surface and enters the inlet ofthe pump. After having been passed through the pump, the cooling liquidis passed out of the outlet of the pump and further out through the tubeoutlet connection 16. The figure also shows a lid 17 for the reservoir.The flow of the cooling liquid inside the reservoir and trough the pumpmay be further optimized in order to use as little energy as possiblefor pumping the cooling liquid, but still having a sufficient amount ofheat from the heat exchanging surface being dissipated in the coolingliquid. This further optimization can be established by changing thelength and shape of the tube connection inlet within the reservoir,and/or by changing the position of the pump inlet, and/or for instanceby having the pumping device placed in the vicinity and in immediatethermal contact with the heat exchanging surface and/or by providingchannels or segments inside the reservoir.

In this case, an increased turbulence created by the pumping device isused to improve the exchange of heat between the heat exchanging surfaceand the cooling liquid. Another or an additional way of improving theheat exchange is to force the cooling liquid to pass through speciallyadapted channels or segments being provided inside the reservoir or bymaking the surface of the heat exchanging surface plate inside thereservoir uneven or by adopting a certain shape of a heat sink withsegments. In the figure shown, the inner surface of the heat exchangingsurface facing the reservoir is plane.

FIG. 8 is a perspective view of the cooling system showing the reservoirhousing 14 with the heat exchanging surface (not shown) and the pump(not shown) inside the reservoir. The tube inlet connection and the tubeoutlet connection are connected to a heat radiator by means ofconnecting tubes 24 and 25 through which the cooling liquid flows intoand out of the reservoir and the heat radiator, respectively. Within theheat radiator 11, the cooling liquid passes a number of channels forradiating the heat, which has been dissipated into the cooling liquidinside the reservoir, and to the surroundings of the heat exchanger. Theair fan 10 blows air past the channels of the heat radiator in order tocool the radiator and thereby cooling the cooling liquid flowing insidethe channels through the heat radiator and back into the reservoir.

According to the invention, the heat radiator 11 may be providedalternatively. The alternative heat radiator is constituted by a heatsink, such as a standard heat sink made of extruded aluminum with finson a first side and a substantially plane second side. An air-fan may beprovided in connection with the fins along the first side. Along thesecond side of the heat sink a reservoir is provided with at least oneaperture intended for being closed by placing said aperture coveringpart of, alternatively covering the whole of, the substantial plane sideof the heat sink. When closing the reservoir in such a way a surface ofthe heat sink is in direct heat exchanging contact with an interior ofthe reservoir, and thus in direct heat exchanging contact with thecooling liquid in the reservoir, through the at least one aperture. Thisalternative way of providing the heat radiator may be used in theembodiment shown in FIG. 8 or may be used as a heat radiator for anotheruse and/or for another embodiment of the invention.

A pumping means for pumping the cooling liquid trough the reservoir mayor may not be provided inside the reservoir at the heat sink. Thereservoir may be provided with channels or segments for establishing acertain flow-path for the cooling liquid through the reservoir. Channelsor segments are especially needed when the inner surface of the heatexchanging surface is plane and/or when the inner walls of the reservoirare smooth and/or if the pump is not situated inside the reservoir. Ineither of the circumstances mentioned, the flow of the cooling liquidinside the reservoir may result in the cooling liquid passing thereservoir too quickly and not being resident in the reservoir for asufficient amount of time to take up a sufficient amount of heat fromthe heat exchanging surface. If channels or segments in the reservoirare to be provided inside the reservoir, the shape and of the channelsand segments may be decisive of whether the reservoir is to be made ofplastic, perhaps by injection molding, or is to be made of metal such asaluminum, perhaps by die casting.

By means of the alternative heat radiator, the heat radiator 11 is notprovided as is shown in the figure with the rather expensive structureof channels leading the cooling liquid along ribs connecting thechannels for improved surface of the structure. Instead, the heatradiator is provided as described as a unit constituted by a heat sinkwith or without a fan and a reservoir, and thereby providing a simplerand thereby cheaper heat radiator than the heat radiator 11 shown in thefigure.

The alternative heat radiator provided as an unit constituted by a heatsink and a reservoir, may be used solely, with or without a pump insidethe reservoir and with or without the segments or channels, for beingplaced in direct or indirect thermal contact with a heat generatingprocessing unit such as CPU or with the heat exchanging surface,respectively. These embodiments of the invention may e.g. be used for areservoir, where the cooling liquid along a first side within thereservoir is in direct heat exchanging contact with the heat generatingprocessing unit such as a CPU and the cooling liquid along a second sidewithin the reservoir is in direct heat exchanging contact with a heatsink. Such a reservoir may be formed such as to provide a larger area ofheat exchanging surface towards the heat generating processing unit suchas a CPU than the area of the heat exchanging surface facing the heatsink. This may e.g. have the purpose of enlarging the area of the heatexchanging surface so as to achieve an improved heat dissipation forme.g. the CPU to the heat sink than that of a conventional heat sinkwithout a reservoir attached. Conventional heat sinks normally onlyexchanges heat with the CPU through the area as given by the area of thetop side of the CPU. A system comprising a liquid reservoir and a heatsink with a fan provided has been found to be a simple, cost optimizedsystem with an improved heat dissipation than that of a standard heatsink with a fan, but without the reservoir. In another embodiment of theinvention, which may be derived from FIG. 8, the air fan and the heatradiator is placed directly in alignment of the reservoir. Thereby, thereservoir housing 14, the air fan 10 and the radiator 11 constitute anintegrate unit. Such an embodiment may provide the possibility ofomitting the connection tubes, and passing the cooling liquid directlyfrom the heat radiator to the reservoir via an inlet connection of thereservoir, and directly from the reservoir to the heat radiator via anoutlet connection of the reservoir. Such an embodiment may even renderthe possibility of both the pumping device of the liquid pump inside thereservoir and the electrical motor for the propeller of the air fan 23of the heat radiator 11 being driven by the same electrical motor, thusmaking this electrical motor the only motor of the cooling system.

When placing the heat radiator on top of the air fan now placed directlyin alignment with the reservoir and connecting the heat radiatordirectly to the inlet connection and outlet connection of the reservoir,a need for tubes will not be present. However, if the heat radiator andthe reservoir is not in direct alignment with each other, but tubes maystill be needed, but rather than tubes, pipes made of metal such ascopper or aluminum may be employed, such pipes being impervious to anypossible evaporation of cooling liquid. Also, the connections betweensuch pipes and the heat radiator and the reservoir, respectively, may besoldered so that even the connections are made impervious to evaporationof cooling liquid.

In the derived embodiment just described, an integrated unit of thereservoir, the heat exchanging surface and the pumping device will begiven a structure establishing improved heat radiating characteristicsbecause the flow of air of the air fan may also be directed along outersurfaces of the reservoir. If the reservoir is made of a metal, themetal will be cooled by the air passing the reservoir after havingpassed or before passing the heat radiator. If the reservoir is made ofmetal, and if the reservoir is provided with segments on the outsidesurface of the reservoir, such cooling of the reservoir by the air willbe further improved. Thereby, the integrated unit just described will beapplied improved heat radiating characteristics, the heat radiationfunction normally carried out by the heat radiator thus beingsupplemented by one or more of the further elements of the coolingsystem, i.e. the reservoir, the heat exchanging surface, the liquid pumpand the air fan.

FIG. 9-10 show an embodiment of a reservoir housing 14, where channels25 are provided inside the reservoir for establishing a forced flow ofthe cooling liquid inside the reservoir. The channels 25 in thereservoir housing 14 lead from an inlet 15 to an outlet 16 like a mazebetween the inlet and the outlet. The reservoir housing 14 is providedwith an aperture 27 having outer dimensions corresponding to thedimensions of a free surface of the processing unit 1 to be cooled. Inthe embodiment shown, the processing unit to be cooled is a CPU 1.

When channels 26 are provided inside the reservoir, the shape of thechannels may be decisive of whether the reservoir is to be made ofplastic, perhaps manufactured by injection molding, or is to be made ofmetal such as aluminum, perhaps manufactured by extrusion or by diecasting.

The reservoir housing 14 or any other parts of the cooling system, whichare possibly manufactured from a plastic material may be “metalized” inorder to minimize liquid diffusion or evaporation of the liquid. Themetal may be provided as a thin layer of metal coating provided oneither or on both of the internal side or the external side of theplastic part.

The CPU 1 is intended for being positioned in the aperture 27, as shownin FIG. 10, so that outer boundaries of the CPU are engaging boundariesof the aperture. Possibly, a sealant (not shown) may be provided alongthe boundaries of the CPU and the aperture for ensuring a fluid tightengagement between the boundaries of the CPU and the boundaries of theaperture. When the CPU 1 is positioned in the aperture 27, the freesurface (not shown) of the CPU is facing the reservoir, i.e. the part ofthe reservoir having the channels provided. Thus, when positioned in theaperture 27 (see FIG. 10), the free surface of the CPU 1 is havingdirect contact with cooling liquid flowing through the channels 26 inthe reservoir.

When cooling liquid is forced from the inlet 15 along the channels 26 tothe outlet 16, the whole of the free surface of the CPU 1 will be passedover by the cooling liquid, thus ensuring a proper and maximized coolingof the CPU. The configuration of the channels may be designed andselected according to any one or more provisions, i.e. high heatdissipation, certain flow characteristics, ease of manufacturing etc.Accordingly, the channels may have another design depending on anydesire or requirement and depending on the type of CPU and the size andshape of the free surface of the CPU. Also. other processing units thana CPU may exhibit different needs for heat dissipation, and may exhibitother sizes and shapes of the free surface, leading to a need for otherconfigurations of the channels. If the processing unit is very elongate,such as a row of microprocessors, one or a plurality of parallelchannels may be provided, perhaps just having a common inlet and acommon outlet.

FIG. 11-1.3 show an embodiment of a heat sink 4, where segments 28 areprovided at a first side 4A of the heat sink, and fins 29 fordissipating heat to the surroundings are provided at the other, secondside 4B of the heat sink. An intermediate reservoir housing 30 isprovided having a recessed reservoir at the one side facing the firstside 4A of the heat sink. The recessed reservoir 30 has an inlet 31 andan outlet 32 at the other side opposite the side facing the heat sink 4.

When segments 28 are provided on the first side 4A of the heat sink, theshape of the segments may be decisive of whether the reservoir, which ismade from metal such as aluminum or copper, is to be made by extrusionor is to be made by other manufacturing processes such as die casting.Especially when the segments 28 are linear and are parallel with thefins 29, as shown in the embodiment, extrusion is a possible andcost-effective means of manufacturing the heat sink 4.

The intermediate reservoir 30 or any other parts of the cooling system,which are possibly manufactured from a plastic material may be“metalized” in order to minimize liquid diffusion or evaporation of theliquid. The metal may be provided as a thin layer of metal coatingprovided on either or on both of the internal side or the external sideof the plastic part.

The recessed reservoir is provided with a kind of serration 33 alongopposite sides of the reservoir, and the inlet 31 and the outlet 32,respectively, are provided at opposite corners of the intermediatereservoir 30. The segments 28 provided at the first side 4A of the heatsink, i.e. the side facing the intermediate reservoir 30, are placed sothat when the heat sink is assembled with the intermediate reservoirhousing (see FIG. 13) the segments 29 run from one serrated side of thereservoir to the other serrated side of the reservoir.

When cooling liquid is forced from the inlet 31 through the reservoir,along channels (not shown) formed by the segments 29 of the heat sink 4and to the outlet 32, the whole of the first side 4A of the heat sinkwill be passed over by the cooling liquid, thus ensuring a proper andmaximized heat dissipation between the cooling liquid and the heat sink.The configuration of the segments on the first side 4A of the heat sinkand the configuration of the serrated sides of the intermediatereservoir housing may be designed and selected according to anyprovisions. Accordingly, the segments may have another design, perhapsbeing wave-shaped or also a serrated shape, depending on any desiredflow characteristics of the cooling liquid and depending on the type ofheat sink and the size and shape of the reservoir.

Also other types of heat sinks, perhaps circular shaped heat sinks mayexhibit different needs for heat dissipation, may exhibit other sizesand shapes of the free surface, leading to a need for otherconfigurations of the segments and the intermediate reservoir. If theheat sink and the reservoir are circular or oval, a spiral-shapedsegmentation or radially extending segments may be provided, perhapshaving the inlet or the outlet in the centre of the reservoir. If animpeller of the pump is provided, as shown in FIG. 15-16, the impellerof the pump may be positioned in the centre of a spiral-shapedsegmentation or in the centre of radially extending segments.

FIG. 14 shows the reservoir housing 14 shown in FIG. 9-10 and the heatsink 4 and the intermediate reservoir 30 shown in FIG. 11-13 beingassembled for thereby constituting an integrated monolithic unit. It isnot absolutely necessary to assemble the reservoir housing 14 of FIG.9-10 and the heat sink 4 and the intermediate reservoir 30 of FIG. 11-13in order to obtain a properly functioning cooling system. The inlet 15and the outlet 16 of the reservoir housing 14 of FIG. 9-10 may beconnected to the outlet 32 and the inlet 31, respectively, of theintermediate reservoir of FIG. 11-13 by means of tubes or pipes.

The reservoir housing 14 of FIG. 9-10 and the heat sink 4 and theintermediate reservoir 30 of FIG. 11-13 may then be positioned in thecomputer system at different locations. However, by assembling thereservoir housing 14 of FIG. 9-10 and the heat sink 4 and theintermediate reservoir of FIG. 11-13 a very compact monolithic unit isobtained, also obviating the need for tubes or pipes. Tubes or pipes mayinvolve an increased risk of leakage of cooling liquid or may requiresoldering or other special working in order to eliminate the risk ofleakage of cooling liquid. By eliminating the need for tubes or pipes,any leakage and any additional working is obviated when assembling thecooling system.

FIG. 15-16 show a possible embodiment of a reservoir according to theinvention. The reservoir is basically similar to the reservoir shown inFIG. 9-10. However, an impeller 33 of the pump of the cooling system isprovided in direct communication with the channels 26. Also, in theembodiment shown, a heat exchanging interface 4 such as a surface madefrom a copper plate, alternatively a plate of another material having ahigh thermal conductivity, is placed between the channels 26 inside thereservoir and the CPU 1 as the processing unit.

The heat exchanging surface 4 is preferably made from a copper platehaving a plane outer surface as shown in the figure, said outer surfacebeing intended for abutting the free surface of the heat generatingcomponent such as the CPU 1 (see FIG. 4). However, also the innersurface (not shown, see FIG. 7) facing the reservoir is plane.Accordingly, the copper plate need no machining other than the shapingof the outer boundaries into the specially adapted shape used in theembodiment shown and drilling of holes for insertion of the bolts. Nomilling of the inner and/or the outer surface need be provided.

The provision of the heat exchanging surface 4 need not be a preferredembodiment, seeing that the solution incorporating the aperture (seeFIG. 9-10) result in a direct heat exchange between the free surface ofthe CPU or other processing unit and the cooling liquid flowing alongthe channels in the reservoir. However, the heat exchanging surfaceenables usage of the cooling system independently on the type and sizeof the free surface of CPU or other processing unit. Also, the heatexchanging surface enables replacement, repair or other intervention ofthe cooling system without the risk of cooling liquid entering thecomputer system as such and possibly without the need for draining thecooling system fully or partly of cooling liquid.

In the embodiment shown, the heat exchanging surface 4 is secured to thereservoir by means of bolts 22. Other convenient fastening means may beused. The heat exchanging surface 4 and thus the reservoir housing 14may be fastened to the CPU 1 or other processing unit by any suitablemeans such as soldering, brazing or by means of thermal paste combinedwith glue. Alternatively, special means (not shown) may be provided forensuring a thermal contact between the free surface of the CPU or otherprocessing unit and the heat exchanging surface. One such means may bethe fastening means shown in FIG. 4 and FIG. 5 or similar fasteningmeans already provided as part of the computer system.

When channels 26 are provided inside the reservoir housing 14, the shapeof the channels may be decisive of whether the reservoir is to be madeof plastic, perhaps by injection molding, or is to be made of metal suchas aluminum, perhaps by die casting.

The reservoir housing 14 or any other parts of the cooling system, whichare possibly manufactured from a plastic material may be “metalized” inorder to minimize liquid diffusion or evaporation of the liquid. Themetal may be provided as a thin layer of metal coating provided oneither or on both of the internal side or the external side of theplastic part.

The impeller 33 (see FIG. 14) of the pump is positioned in a separaterecess of the channels 26, said separate recess having a sizecorresponding to the diameter of the impeller of the pump. The recess isprovided with an inlet 34 and an outlet 35 being positioned opposite aninlet 31 and an outlet 32 of cooling liquid to and from, respectively,the channels 26. The impeller 33 of the pump has a shape and a designintended only for one way rotation, in the embodiment shown a clock-wiserotation only. Thereby, the efficiency of the impeller of the pump ishighly increased compared to impellers capable of and intended for bothclock-wise and counter clock-wise rotation.

The increased efficiency of the impeller design results in the electricmotor (not shown) driving the impeller of the pump possibly beingsmaller than otherwise needed for establishing a proper and sufficientflow of cooling liquid through the channels. In a preferred embodiment,the electric motor is an AC motor, preferably a 12V AC motor, althoughthe impeller is intended for a DC motor. The contradictory use of an ACmotor driving a DC impeller leads to the possibility of an even smallermotor needed for establishing the proper and sufficient flow of coolingliquid through the channels.

The impeller may be driven by an electrical motor at any voltage commonin public electrical networks such as 110V or 220V. The power supply ofthe computer system converts the high voltage AC power to low voltage DCpower. Thus, the impeller of the pump may be driven by an AC or a DCelectrical motor. As mentioned, preferably the impeller of the pump isdriven by an AC electrical motor. Although being technically unnecessaryto use an AC electrical motor and being electrically disadvantageous touse an AC electrical motor in a computer system supplying DC electricalpower, this may be accomplished by converting part of the DC electricalpower of the power supply of the computer system to AC electrical powerfor the AC motor of the pump. However, in the embodiment shown, theimpeller of the pump is driven by a 12V electrical motor.

FIG. 17 shows a preferred possible embodiment of a reservoir accordingto the invention. The reservoir housing 14, as shown in FIGS. 17 and 20,is in the form of a double-sided chassis configured to mount anelectrical motor. The reservoir housing 14 has basically the samefeatures as the reservoir housing shown in FIG. 15-16. In the embodimentshown, the reservoir substantially has a conical, circular configurationand is provided with stiffening ribs 36 extending axially along theexterior of the reservoir housing 14.

Other shapes such as cylindrical, circular, or conical rectangular orcylindrical, rectangular or even oval or triangular shapes may beadopted, when designing and possibly injection molding or casting thereservoir. The dimension of the embodiment shown is approximately 55 mmin diameter and also 55 mm in axial extension.

The reservoir housing 14 has a recess 40 in the centre on the upper sideof the reservoir. The recess 40 is intended for accommodating a stator37 of an electrical motor driving an impeller 33 of the pump, saidimpeller being attached to a shaft 38 of a rotor 39 of the electricalmotor. The recess has an orifice 41, four sidewalls 42, a bottom 43 anda circular jacket 44 extending from the bottom 43 of the recess 40 andoutwards towards the orifice 41 of the recess 40. The interior (see FIG.20) of the jacket 44 is intended for encompassing the rotor 39 of thepump. As shown in FIG. 20, the impeller 33 is housed in a recess on theunderside of the reservoir housing 14, the recess being an extension ofthe interior of the jacket 44.

Thereby, a liquid-proof division is made between the rotor 39 of themotor, said rotor 39 being placed inside the interior of the jacket 44and being submerged in the cooling liquid, and the stator 37 of thepump, said stator 37 being positioned in the recess 40 and surroundingthe exterior of the jacket 44. Accordingly, the stator 37 need not besealed against the cooling liquid, because the recess 40 together withthe jacket 44 ensures the stator staying dry from the cooling liquid,but the stator 37 still being capable of driving the rotor 39, whenbeing supplied with electrical power from a power supply (not shown) ofthe computer system.

Along an outer circumferential extension, the reservoir housing 14 isprovided with protrusions 45 extending outwardly from thecircumferential extension. The protrusions are intended for cooperatingwith a clip (see description below) for fastening the reservoir housing14 to the CPU or other processing unit of the computer system. Theprotrusions 45 are shown as a plurality of singular protrusions.Alternatively, the protrusions may be only one continuous protrusionextending outwardly and around the circumferential extension.

The reservoir housing 14 may also be provided with an inlet (not shown)and an outlet (not shown) for the cooling liquid. The inlet and theoutlet are provided along a surface of the reservoir facing downward andinwards when seen in the perspective view of the drawing. The inlet andthe outlet lead to a radiator (not shown) intended for cooling thecooling liquid after having been heated by the processing unit via aheat exchanging surface (see description below).

The radiator may be placed nearby or distant from the reservoir housing14, depending on the set-up of the computer system. In one possibleembodiment, the radiator is placed in the immediate vicinity of thereservoir, thereby possible excluding any tubing extending between theradiator and the inlet and the outlet, respectively. Such embodimentprovides a very compact configuration of the entire cooling system,namely a monolithic configuration where all elements needed for thecooling system are incorporated in one unit.

In an alternative embodiment, the reservoir housing 14 itself alsoconstitutes the radiator of the cooling system. In such embodiment, aninlet and an outlet are not needed. If the reservoir is made of a metalsuch as copper or aluminum or other material having a high thermalconductance, the cooling liquid, after having been heated by theprocessing unit via a heat exchanging surface 8 see description below)may radiate the heat via the exterior surface of the reservoir housing14 itself. In such embodiment, the ribs 36 along the exterior surface ofthe reservoir housing 14 may also, or may instead, function as coolingfins. In such embodiment, the fins will have a smaller dimension thanthe transverse dimension of the ribs 14 shown in FIG. 17, and the numberof fins will be greater than the number of fins shown in FIG. 17.

An impeller 33 of the pump of the cooling system is provided in directcommunication with a pump chamber 46 formed by impeller cover 46A havingan outlet 34 provided tangentially to the circumference of the impeller33. Thus, the pump functions as a centrifugal pump. The inlet of thepump chamber 46 is the entire opening into the cavity that the pumpchamber configures, said cavity being in direct communication with theinterior of the reservoir housing 14 as such. An intermediate member 47is provided between the pump chamber 46 together with the interior ofthe reservoir and a heat exchanging interface 4. The intermediate member47 is provided with a first passage 48 for leading cooling liquid fromthe pump chamber 46 to a thermal exchange chamber 47A provided at theopposite of the intermediate member 47. The intermediate member 47 isprovided also with a second passage 49 for leading cooling liquid fromthe thermal exchange chamber 47A provided at the opposite of theintermediate member 47 to the interior of the reservoir housing 14.Thus, the area enclosed between the underside of the reservoir housing14 and the heat exchange surface 4 constitutes an enclosed space forcirculating the cooling liquid therethrough. The enclosed spaced isdivided into two separate chambers by the impeller cover 46A and theintermediate member 47, as shown in FIG. 20. The impeller cover 46Ainterfaces with the recess on the underside of the reservoir 14 todefine the pump chamber 46 which houses the impeller 33, while theintermediate member 47 and the heat exchange surface 4 together definethe thermal exchange chamber 47A.

In the embodiment shown, a heat exchanging interface 4 such as a surfacemade from a copper plate, alternatively a plate of another materialhaving a high thermal conductivity, is placed in thermal communicationwith the thermal exchange chamber (not shown) at the opposite side ofthe intermediate member 47.

The heat exchanging interface 4 is preferably made from a copper platehaving a plane outer surface (not shown) at the opposite side as theside shown in the figure, said outer surface being intended for abuttingthe free surface of the heat generating component such as the CPU (seeFIG. 4). The inner surface facing the thermal exchange chamber (notshown) at the opposite side of the intermediate member 47 is providedwith pins 4A extending from the base of the copper plate and into thethermal exchange chamber (not shown) at the opposite side ofintermediate member 47. The pins 4A constitutes an uneven surface andmay either be provided during casting of the copper plate or may beprovided by means of milling or other machining process of a copperplate. The pins provide a network of channels across the inner surfaceof the heat exchanging interface, along which network the cooling liquidis intended to flow.

Alternatively, also the inner surface of the copper plate facing thereservoir is plane. In this alternative embodiment, the copper plateneed no machining other than the shaping of the outer boundaries intothe specially adapted shape used in the embodiment shown. No milling orother machining process of the inner and/or the outer surface need beprovided, when both the outer surface and the inner surface is plane.

The provision of the heat exchanging interface 4 need not be a preferredembodiment, seeing that the solution incorporating the aperture (seeFIG. 9-10) result in a direct heat exchange between the free surface ofthe CPU or other processing unit and the cooling liquid flowing alongthe channels in the reservoir. However, the heat exchanging interfaceenables usage of the cooling system independently on the type and sizeof the free surface of CPU or other processing unit. Also, the heatexchanging interface enables replacement, repair or other interventionof the cooling system without the risk of cooling liquid entering thecomputer system as such and possibly without the need for draining thecooling system fully or partly of cooling liquid.

In the embodiment shown, the heat exchanging interface 4 is secured tothe intermediate member 47 by means of gluing or other means ensuring aproper and liquid-tight fastening of the heat exchanging interface withthe intermediate member. Any other suitable and convenient means (notshown) for securing the heat exchanging interface to the intermediatemember may be envisaged.

The heat exchanging interface and thus the reservoir is fastened to thetop of the CPU by means of a clip 50. The clip 50 has a circularconfiguration and has four legs 51 extending axially from the circularconfiguration. The four legs 51 are provided with footing 52 and thefootings 52 are provided with holes 53. The clip 50 is intended forbeing displaced around the exterior of the reservoir housing 14 andfurther axially to the protrusions 45 of the reservoir housing 14.

The clip 50, after having been placed around the reservoir housing 14,is fastened to the motherboard of the computer system by means of bolts(not shown) or the like fastening means extending through the holes 53in the footings 52 and further though corresponding holes in themotherboard. The corresponding holes in the motherboard are preferablyholes already available in the motherboard in the vicinity of the CPUand the socket of the CPU, respectively. Accordingly, the legs 51 andthe footings 52 of the clip 50 are specially designed in accordance withthe already provided holes in the motherboard.

Alternatively, the heat exchanging interface 4 and thus the reservoirhousing 14 may be fastened to the CPU or other processing unit by anyother suitable means such as soldering, brazing or by means of thermalpaste combined with glue. Alternatively, special means (not shown) maybe provided for ensuring a thermal contact between the free surface ofthe CPU or other processing unit and the heat exchanging interface. Onesuch means may be the fastening means shown in FIG. 4 and FIG. 5 orsimilar fastening means already provided as part of the computer system.

When stiffening and/or cooling fins 36 are provided at the exterior ofthe reservoir housing 14, the shape of and the number of fins may bedecisive of whether the reservoir is to be made of plastic, perhaps byinjection molding, or is to be made of metal such as aluminum, perhapsby die casting. Also, the purpose of the fins i.e. just for stiffeningthe reservoir, or also or instead for cooling purposes, may be decisiveof whether the reservoir is to be made of plastic, perhaps by injectionmolding, or is to be made of metal such as aluminum, perhaps by diecasting.

The reservoir housing 14 or any other parts of the cooling system, whichare possibly manufactured from a plastic material may be “metalized” inorder to minimize liquid diffusion or evaporation of the liquid. Themetal may be provided as a thin layer of metal coating provided oneither or on both of the internal side or the external side of theplastic part.

The impeller 33 of the pump has a shape and a design intended only forone way rotation, in the embodiment shown a clock-wise rotation only.Thereby, the efficiency of the impeller of the pump is highly increasedcompared to impellers capable of and intended for both clock-wise andcounter clock-wise rotation.

The increased efficiency of the impeller design results in the electricmotor (not shown) driving the impeller of the pump possibly beingsmaller than otherwise needed for establishing a proper and sufficientflow of cooling liquid through the channels. In a preferred embodiment,the electric motor is an AC motor, preferably a 12V AC motor, althoughthe impeller is intended for a DC motor. The contradictory use of an ACmotor driving a DC impeller leads to the possibility of an even smallermotor needed for establishing the proper and sufficient flow of coolingliquid through the channels.

The impeller may be driven by an electrical motor at any voltage commonin public electrical networks such as 110V AC power or 220V AC power.The power supply of the computer system converts the high voltage ACpower to low voltage DC power. Thus, the impeller of the pump may bedriven by either an AC or a DC electrical motor. As mentioned,preferably the impeller of the pump is driven by an AC electrical motor.Although being technically unnecessary to use an AC electrical motor andbeing electrically disadvantageous to use an AC electrical motor in acomputer system supplying DC electrical power, this may be neverthelessbe accomplished by converting part of the DC electrical power of thepower supply of the computer system to AC electrical power for the ACmotor of the pump.

In every aspect of the invention, where an AC motor is used for drivingan impeller from a DC motor, although this way of configuring a pump iscontradictory, the following preferred mode of operation is establishedfor alleviating the disadvantages:

In order to be able to control direction of rotation of the impellerattached to the rotor and to optimize the conditions of maximum averagetorque value during starting, i.e. from zero speed up to the synchronousspeed, an electronic control circuit is used. The electronic controlcircuit comprises a processing unit, which drives a static power switch,constituted for example by a triac arranged in series between thealternating-voltage power, which is obtained from the DC power supply ofthe computer system, and the AC motor. The same series network alsoincludes a detector for the current I which flows through the triac andthen through the AC motor. The output of the current detector is aninput signal for the electronic processing unit.

The electronic control circuit may also comprise a number or sensorssuitable for detecting the position and polarity of the permanentmagnets comprised in the rotor of the AC motor, both when the rotor ismoving and when it is in particular operating conditions, or when it ismotionless or stalled at zero speed. The number of position sensors maybe Hall sensors, encoders or optical or electromechanical sensorscapable of establishing and/or measuring the position of the rotor. Theoutput signal from the number of position sensors is an input signal forthe electronic processing unit.

Alternatively, the output signal from the position sensor may be phaseshifted by means of an electronic phase shifting circuit before theoutput signal is sent to the input of the electronic processing unit.

A third signal may be input to the processing unit, said third signalenabling the processing unit to detect the polarity of the AC voltageapplied to the AC motor. However, the third signal is not compulsory.

The signals input to the electronic processing unit are converted intodigital form and after being processed by the processing unit, an outputsignal is provided by the processing unit. The output signal is used forclosing or opening the static switch constituted by a triac arranged inseries with the AC motor.

In the electronic processing unit, the current signal provided by thecurrent sensor enters a zero-crossing detector which provides in outputa logical “1” signal indicating that said current approaches zero with apositive or negative deviation from the zero value of said current. Thisdeviation depends on the type of motor used and on its application, aswell as on the type of static power switch being used. The signalarriving from the position sensor enters a phase-shift and processingcircuit the output whereof is 1 or 0 according to the position andpolarity of the rotor.

In the electronic processing unit, the phase shifted position signal aswell as the signal processed from the AC voltage, enter an electroniclogic XOR gate which outputs a “1” signal if the digital value of the ACvoltage is equal to “0” and the digital value of the phase shiftedposition signal is equal to “1” or the digital value of the AC voltageis equal to “1” and the digital value of the phase shifted positionsignal is equal to “0”.

The output of the zero-crossing detector and the output of the XOR gate,thus in digital form, enter an electronic logic AND gate which providesin output the control signal for closing or opening the static powerswitch.

The AND gate with two inputs and the signal processing system allowdetermining two conditions: 1) the AC voltage signal is positive, thecurrent is proximate to zero, and the rotor rotation angle is between 0degrees and 180 degrees; 2) the AC voltage signal is negative, thecurrent is proximate to zero, and the rotor rotation angle is between180 degrees and 360 degrees. These two conditions provide the samerotation direction of the rotor of the AC motor.

FIG. 18 shows an embodiment of an AC motor in which one stator pole 54is longer than the other stator pole 55 by an amount indicated by I.With this configuration the permanent-magnet rotor 39 with an ideal line56 separating the north N and the south S of the rotor, is positioned sothat the ideal line 56 do not coincide with the median axis 57 of thestator 37, but so that the ideal line 56 is tilted by a certain angle.alpha. in respect to the median 57 of the stator 37.

Two energizing windings 58, 59 are provided on the two poles 54,55 ofthe stator 37, respectively, and the energizing windings are connectedin series and are powered, through terminals (not shown), by an AC powersource. With this configuration of the AC motor, the motor is able tostart more easily in an intended rotational direction of the rotor.

In a preferred embodiment of the invention, the control electronicssupplies the AC motor with only a half-wave voltage signal during startup, thereby providing torque pulses to the rotor. Since only a half-wavevoltage signal is supplied to the motor, the torque pulses are alwaysunidirectional and will therefore force the rotor to start rotating in arequired direction. The required direction of rotation is determined bythe design of the impeller attached to the rotor and by polarity of thehalf-wave voltage signal.

After some amount of time, in which a number of half-wave voltagesignals has been supplied to the motor, the rotor will stop rotating ata certain position e.g. as shown in the figure. Thus, the rotor isbrought into a determined steady state position that is independent ofits start position. Subsequent to this process, the AC motor is suppliedwith a full-wave voltage signal that will accelerate the rotor until themotor enters synchronous operation, that is, when the rotor rotates withthe same cyclic frequency as the frequency of the AC voltage source.

The initial polarity of the AC voltage signal is determinative for theresulting direction of rotation of the rotor, thus if the initialvoltage is positive with an increasing amplitude, the rotor will startrotating in one direction, whereas if the voltage is negative with adecreasing amplitude, the rotor will start rotating in an oppositedirection.

The number of half-waves required for bringing the rotor into adetermined steady state position, where the rotor stops rotating,depends on the characteristics of the motor such as moment of inertiaand the external load applied to the rotor. Thus, the number ofhalf-waves required is based on empirical analysis of a particular motorin particular load conditions.

The half-wave voltage signal and the corresponding half-wave currentsignal supplied to the motor will have an appearance as shown in FIG.19.

In an alternative embodiment the control electrics used to drive the ACmotor shown if FIG. 18 is configured so that that the controlelectronics dictates the AC motor to stop at a predetermined position bysupplying the motor with a number of half-wave voltage signalssubsequent to the synchronous operation in which the motor was suppliedwith a full-wave voltage signal. Thus, at the time the motor needs to bestarted again, the rotor is already in a position so that only thepolarity of the full-wave AC voltage signal supplied to the motor mustbe chosen so that the resulting direction of rotation of the rotor is inconformity with the terminal position of the rotor at the lastoperation.

According to this method, the initial step of bringing the rotor into adetermined steady state position by supplying the motor with a number ofhalf-wave voltage signals is not required. Even in the alternative, itwill be possible to both terminate the full-wave power supply with anumber of half-wave voltage signals as well as commencing the full-wavepower supply by initially supplying the motor with a number of half-wavesignals. However, this is more cumbersome, but nevertheless more safe.

FIG. 19 shows a voltage signal V and a current signal I applied to theAC motor as well as the position signal of the rotor. Initially therotor stands still, which is represented by the straight line L. Theelectronic control circuit controls the static power switch so that thevoltage signal V and the current signal I are present as half-waves.Thus, the rotor receives torque pulses due to the current-voltagecombination; these pulses are always one-way directional and tend tostart the rotor moving in the required direction. Subsequent to thestart-up phase, the rotor enters into its synchronous operation.

Thus, an AC signal is generated, preferably a 12 V AC signal, possiblyby means of digital electric pulses from the 12 V DC power supply of thecomputer's power supply. Based on a possible sensor output relating tothe impeller position, a decision is made of how to initiate the ACpower signal, i.e. with a negative or positive half-wave, and by doingmaking sure the impeller starts in the same rotational direction eachtime and thus the performance benefits of the AC pump is similar tothose of a DC pump.

Alternatively, the magnetic field sensor is omitted, and instead ofreading the impeller position, the impeller is forced to be in the sameposition every time the impeller starts. To be sure the impeller is in adefined position before start, a signal is supplied to the stator of theAC motor for a defined period of time. The signal is supplied perhapsthree times in a row according to the curvature of the electrical powersource. The pulses must be within the same half-wave part of a signalperiod. The frequency of the pulsed signal is arbitrary, but may be50/60 Hz, although, despite the fact that under normal circumstances anAC pump being driven by the AC signal from the power outlet of thepublic electrical power network and transformed from 230/115 V to 12Vwould not function, as there is no chance of changing the sine signalfrom the public network.

By this way the impeller will be forced to the right polarity beforestart, and the pump will start turning the impeller in a defined way ofrotation when the power signal full-wave is supplied. The full-wavepower signal, which is supplied, must start in the opposite signalhalf-wave amplitude than that of the initial half-wave pulses, that wassupplied before start of the full-wave power signal.

The invention has been described with reference to specific embodimentsand with reference to specific utilization, it is to be noted that thedifferent embodiments of the invention may be manufactured, marketed,sold and used separately or jointly in any combination of the pluralityof embodiments. In the above detailed description of the invention, thedescription of one embodiment, perhaps with reference to one or morefigures, may be incorporated into the description of another embodiment,perhaps with reference to another or more other figures, and vice versa.Accordingly, any separate embodiment described in the text and/or in thedrawings, or any combination of two or more embodiments is envisaged bythe present application.

What is claimed is:
 1. A liquid cooling system for cooling aheat-generating component of a computer, comprising: a double-sidedchassis adapted to mount a pump configured to circulate a coolingliquid, the pump comprising a motor with a stator and an impeller, theimpeller being positioned on one side of the chassis and the statorbeing positioned on an opposite side of the chassis and isolated fromthe cooling liquid; a reservoir adapted to pass the cooling liquidtherethrough, the reservoir including: a pump chamber including theimpeller; and a thermal exchange chamber formed below the pump chamberand vertically spaced apart from the pump chamber, the pump chamber andthe thermal exchange chamber being separate enclosed chambers that arefluidly coupled together by one or more passages; a heat-exchanginginterface removably coupled to the reservoir, the heat-exchanginginterface forming a boundary wall of the thermal exchange chamber andconfigured to be placed in thermal contact with a surface of theheat-generating component; a heat radiator adapted to pass the coolingliquid therethrough, the heat radiator being fluidly coupled to thereservoir and positioned at a location horizontally spaced apart fromthe heat-generating component, the heat radiator being configured todissipate heat from the cooling liquid; a fan configured to direct airthrough the heat radiator, the fan being driven by a motor separate fromthe motor of the pump; and a control system configured to independentlycontrol a speed of the pump and a speed of the fan.
 2. The coolingsystem of claim 2, wherein the chassis shields the stator from thecooling liquid in the reservoir.
 3. The cooling system of claim 1,wherein the heat exchanging interface includes a first side and a secondside opposite the first side, and wherein the heat-exchanging interfacecontacts the cooling liquid in the thermal exchange chamber on the firstside and the heat-exchanging interface is configured to be in thermalcontact with the surface of the heat-generating component on the secondside.
 4. The cooling system of claim 3, wherein the first side of theheat-exchanging interface includes features that are adapted to increaseheat transfer from the heat-exchanging interface to the cooling liquidin the thermal exchange chamber.
 5. The cooling system of claim 4,wherein the features include at least one of pins or fins.
 6. Thecooling system of claim 1, wherein the impeller is positioned in thepump chamber.
 7. The cooling system of claim 1, wherein the impellerincludes a plurality of curved blades.
 8. A cooling system for acomputer system, comprising: a centrifugal pump adapted to circulate acooling liquid, the pump including: a curved impeller exposed to thecooling liquid; and a stator isolated from the cooling liquid; areservoir configured to be thermally coupled to a heat-generatingcomponent of the computer system, the reservoir including: a thermalexchange chamber adapted to be positioned in thermal contact with theheat-generating component; a separate pump chamber vertically spacedpart from the thermal exchange chamber and coupled with the thermalexchange chamber through one or more passages configured for fluidcommunication between the pump chamber and the thermal exchange chamber;a heat radiator fluidly coupled to the reservoir and positioned at alocation spaced apart from the heat-generating component; a fan attachedto the heat radiator, wherein a speed of the fan is configured to bevaried independent of a speed of the pump; and a control systemconfigured to independently adjust a speed of the pump and a speed ofthe fan to provide a desired cooling capacity.
 9. The cooling system ofclaim 8, wherein the thermal exchange chamber includes a heat-exchangeinterface configured to be placed in thermal contact with theheat-generating component.
 10. The cooling system of claim 8, whereinthe control system is configured to independently control the speed ofthe pump and the speed of the fan to minimize noise while providing thedesired cooling capacity.
 11. The cooling system of claim 10, wherein,if the fan generates more noise than the pump, the control systemreduces the speed of the fan before the speed of the pump to reducenoise, and if the pump generates more noise than the fan, the controlsystem reduces the speed of the pump before the speed of the fan toreduce noise.
 12. The cooling system of claim 8, wherein the controlsystem is configured to determine the desired cooling capacity based ona performance parameter of the heat generating component.
 13. Thecooling system of claim 12, wherein the performance parameter is one ofan operating load or an operating temperature of the heat-generatingcomponent.
 14. The cooling system of claim 8, wherein the control systemconfigured to determine the desired cooling capacity based on at leastone of an operating load or an operating temperature of theheat-generating component.
 15. The cooling system of claim 8, whereinthe control system is configured to determine the desired coolingcapacity based on a type of computer processing taking place in theheat-generating component.
 16. The cooling system of claim 8, whereinthe control system is configured to reduce the speed of the fan beforethe speed of the pump to reduce noise if the fan generates more noisethan the pump, and reduce the speed of the pump before the speed of thefan to reduce noise if the pump generates more noise than the fan. 17.The cooling system of claim 8, wherein the control system is configuredto select a rotational direction of the impeller.
 18. The cooling systemof claim 8, wherein the control system is configured to determine anangular position of the rotor.